Julius Caesar was the famous ancient Roman general who famously crossed the Rubicon River in 49 BCE, an act that led to a civil war in Rome. The phrase "crossing the Rubicon" has since become a metaphor for making irreversible decisions. Caesar's crossing was significant as it defied the Roman Senate's authority, challenging the existing political order. This bold move led to his ascent to power, eventually establishing him as dictator. His actions and subsequent assassination in 44 BCE catalyzed the transformation of the Roman Republic into the Roman Empire, profoundly impacting Western history and governance.